Electro-optic light beam control for displaying and printing



l-il (I. Chang wait d'oiey, New York internntlonal En ines; MachinesCorporation Armonilt, New York a cea'gyoratinn at New Yorkl-lLlEUiHO-OETHJ HGH'E' BEAM CONTROL FUR Z1553 AYENG AND l TMNTENG i STDEFLECTOR I56] References Cited UNITED STATES PATENTS 3,220,0l3 l l/l965Harris 346/107 Primary Examiner-John M. Horan l Auurnuy- Hunil'mundjancin and Edward S. (iershuny ABSTRACT: Electro-optic means forcontrolling the deflection ofa beam oflight to efi'ect the display orprinting ofinformation. A first deflector deflects a beam of lightthrough a selected portion of a character mask to produce acharactershaped beam A second deflector deflects the charactershapedbeam to a selected location on a light sensitive medium. The deflectioncontrol means for the second deflector adds two signals together toproduce a resultant signal indica tive of the amount of deflectionrequired of the second deflector to direct the character-shaped beam tothe selected location on the light sensitive medium.

2N0 DEFLECTOR CHARACTER SELECTION WAGE DEFLECTIOH H-V DRIVER PaieniedGd. 397% 3,532,33

Sheet I of 3 PREGR ART 3R0 UEFLECTOR 1 ST DEFLECTOR 2ND DEFLECTOR 5CHARACTER H-V IMAGE I H-V SELECTION DRIVER DEFLECHON W W 2ND DEFLECTOR 1ST DEFL'ECTOR H H-V 15 H-V omv ER 0mm CHARACTER SELECTION IMAGEDEFLECTION n INVENTOR DAVID C CHANG ATTORNEY Pmemed @ci. 5, 3979 Sheet2ND DEFLECTOR 00 2 L A T R N 0 2' R W 8 0 cl IL H Al R EL R E VvVERTICAL DRIVER 1ST DEFLECTOR HORIZONTAL DRWER SWITCH CONTROL VERTICAL mDRIVER I swncu CONTROL 1 T W F HORIZONTAL DRIVER VERTICAL DRIVER 1SWITCH comm swncu CONTROL Sheet IIIIWIIII I IMAGE DEFLECTION VERTICALyaiemed @m. 5, HQYQ A HORIZONTAL DWF.

HORIZONTAL .CHARACTER suecnom HORIZONTAL IMAGE DEFLECTION nf vc bELEC'iltO-UlTHC Lilli-l1 BEAM CONTROL FOR DiSPLArlNG AND PillN'liNG This"ivention relates to display and printing mechanisms, and moreparticularly to mechanisms employing a light beam devices forcontrolling it to effect the display or printing cl" information at highspeeds.

Reissue U.S. i at. No. lie. 26,l70 lay-Thomas J. Harris, reissuedib'iorch 7, i967, shows an apparatus which displays c. .arzictcrsselectively on a display medium by means of light. A boom of light whichhas boon collimated and polarized is deflected upon a chnractcr mask.The character mark is generally opaque but has transparent portions inthe form of characters. The light passing through any character portionis thcn deflected to a common point, and it then deflected again to anyselected location on a display or light sensitive medium.

it is well-known to those sitillcd in the art that the intensity oflight will be diminished each time that it passes from one medium toanother. This is because, at the boundary between two media, some of thelight will generally be reflected back from the boundary instead of allof the light being passed through it. Also, the length of the paththrough which the light must? travel will tend to affect its intensity.

An obicct or" this invention is to provide an improved display orprinting mechanism. 7

Another objcct is to provide an improved mechanism in which the lightthat impinges upon a display or light sensitive medium is of greaterintensity. 1

Still another object is to accomplish the above in a manner that willgenerally be less expensive than prior art apparatus.

The foregoing and other objects are accomplished in accordance with oneaspect of this invention by providing apparatus which utilizes only twodeflector stages. The first deflector stage will deflect an incomingbeam of light through. the transparent portion of a'charactcr masltwhich representsa sclcctcd character. The second dcflcctor stage willdeflect the light which passes through lhc transparent character portionof the character mask directly onto any selected location on a displayor light sensitive medium The second deflection is accomplished byadding together two digital signals, one of which represents thelocation of the selected character on the character mask, and the otherof which represents the sclcctcd location on the display or lightsensitive mcdium. This invention requires adding means for itsoperation, while the prior art referred to above docs not. However, itis well known that devices of this nature arc'oftcn used as outputdevices for data processing machines, and therefore the necessary addingmeans will often already bc available.

A significant feature of this invention is its elimination of one or thedeflector stages used in the prior art described above. One of theadvantages of this feature is that this invenlion will generally be lessexpensive to implement than the prior art. Another significant advantageis that the beam of light will lravcrsc fcwcr boundaries in the pathbetween its source and its destination. Also, the total length of thepath traversed by the light will gcncrally be decreased. For therereasons, tin: intensity of the light impinging, upon the display orlight sensitive medium will be greater than in the prior art.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulnrdescription of preferred embodiments ofthc invcntion, as illustrated inthe accompanying drawings.

' in the drawings:

H 5. is a schematic drawing ofa prior on device.

MG. 2 is a schematic drawing of deflection apparatus incorporating thisinvcntion.

MG. 3 is similar to FIG. 2 but shows two deflectors through which thelight passes, each deflector having both means for deflecting the beamvertically to any one of a plurality of selected points, and means fordeflecting it horizontally to any selected point.

HG. l is a side elcvational view of the vertical deflection mechanismfor the first dcflcctor in H0. 3. and the mechanism for dclivcring thelight beam thcrcto.

H6. 5 is a plan view of the horizontal deflection mechanism for thefirst deflector oil-K13.

H6. 6 is a side elevational view of the vertical deflection,

mechanism for th'e second deflector in FIG. 3, and also showing themanner in which two signals are added to produce a resultant deflectionsignal.

H6. 7 is a plan vicw of the horizontal deflection mechanism for thesecond deflector of HO. 3, and also showing the manner in which twohorizontal deflection signals are added to produce the resultanthorizontal deflection signal.

Referring to FIG. 1, the prior art device described in U.S. Pat. No. Re.26,170 is shown. A beam l of monochromatic, collimatcd. and linearlypolarized light is supplied from any suitable source, not shown. Thelight beam 1 passes through a first deflector 2 which is operable todeflect the beam to a point in alignment with any character 3 on acharacter mask 4. This mask in generally opaque but its characterportions are transparent so the beam may pass through such portion andassume the shape of the character. The character-shaped beam then passesthrough a second deflector 5 which is similar to the first deflector butneutralizes the deflection induced by the latter so the beam is returnedto a path corresponding to that at which it was first received. A thirddeflector 6 receives the light beam from the second deflector anddirects it to any selected point on the surface of adisplay or lightsensitive member 7. Deflectors 2 and 5 utilize a commonhorizontalvertical driver 8 in a manner described more fully in U.S.Pat. No. Re.26,l70. Said reissue U.S. Pat. No. Re.26,l is hercbyincorporated herein by this reference. Another horizontal-verticaldriver 9 controls the deflection cfl'ected by deflector 6.

Referring to FIG. 2, wherein apparatus embodying this invention isshown, it will be seen that only two deflectors 10, ll are used. Thefirst deflector l0 deflects a beam 12 of monochromatic, collimated andlinearly polarized light to a point in alignment with any character on acharacter mask 13.

The light beam. which is of small cross-scctional area, may be suppliedby a laser but could also be supplied by carbon or mercury arc lampswith appropriate filters, polarizers, and col- Iimating means. Thecharacter-shaped beam then passes through the second deflector H bywhich it is directed to any selected point on the surface of a displayor light sensitive medium i l. The amount of deflection effected by thefirst deflector it) is controlled by a horizontal-vertical driver l5 inexactly the same manner as the prior art described above with respect toFIG. I. The amount of deflection effected by the scconddcflector i1 iscontrolled by horizontal-vertical driver to. Driver 16 receives itsinput from summing means 17 which combines a digital signal representingthe location of the character that was selected on the mask 13 with adigital signal representing the selected location on the display orlight sensitive medium M..The summing means 17 will hereinafter bereferred to as an adder. However, as will be described in more detailbelow, it must be recognized that the adder I? may cither performaddition or subtraction operations depending upon other parameters ofthe apparatus.

As shown in FIG. 3, the first dcflcctor comprises a unit H0 whichoperates to deflect the light beam 12 vertically to any one of severallevels between the level ill at which the beam is received and a higherlevel lll2. It also includes a unit 1E4 which is opcrablc either to passa light beam from unit H0 without deflection or to deflect the beamhorizontally to any one of several paths between zero-dcflcction pathsH5 and maximum deflection paths 116. it will be seen that thc number ofpaths over which the light beam may be dircctedto the mask 13 is equalto the product of the beam levels produced by unit Hi0 and thehorizontal deflections produced by unit 1 l4. The second deflectorfunctions in a manner similar to the first. The character-shaped lightbeams from the mask 13 first pass through a vertical deflection unit 117and then a horizontal deflection unit 138. Unit 117 can pass the lightbeam without deflection or it can deflect the light beam verticallyupwards. Unit H8 also can pass the light beam without deflection. or itcan deflect the light beam horizontally in a direction o the drawing.The beam leaving the unit Elli engages the .1 i on which information isdisplayed or printed. in Ll preferred embodiment of this invention,character selec- 'ion information will be stored in two registers 32?and i120. "mister will contain a representation of the amount of caldeflection of the light beam 1'4 that is needed for the n to passthrough the sclectcd character. Register 3120 will containrepresentation of the amount of horizontal deflec non that is requiredof the li ght her-1m 12. The information contained in egisters M") andlit? will be utilized to control, ectiveiy, vertical driver 21 andhorizontal driver 127., so that the first deflector lit), lid willproperly deflect the incomir light beam 12 to the selected character onthe mask crs i113 and il -3 will contain, respectively, vertical iondata and horizontal deflection data pertaining to a 'MJCCiCLl locationon the display or light sensitive medium M. in order to ensure that thebeam of light leaving deflection unit ill? or: deflected to the selectedlocation on medium M, the amount oi'dcflection introduced by the firstdeflector H0, 'nust be taken into consideration. Vertical deflectioninuced by deflection unit llfl is taken into consideration by adder i213winch combines the data contained in registers Hi9 and H3 to produce aresultant vertical deflection that is rcn'uired of deflection unit H7 inorder that the light beam a-.ill be at the proper vertical level when itimpinges upon the medium l The output of adder 125 is fed to the inputof vertical driver 327 which controls the amount of deflectionintroduced by deflection unit H7. Similarly. the horizontal deflectionintroduced by deflection unit ll-l is taken into con sideration byadder 1. .6 which combines the horizontal character selection data inregister l2) with the horizontal image deflection data in register 124to produce a resultant output indicative of the amount of horizontaldeflection that must be introduced by deflection unit 213. The output ofadder i2; is fed to horizontal drivcr i215 which controls the amount ofdeflection introduced by deflection unit 1153. The character selectionand image deflection information which is fed into registers ill), i120.i123 and 124 may come from any suitable source, not shown Examples ofsources of this data would be a typewriter, a card or tape reader, acomputer, etc. it will he recognized by those skilled in the art thatregisters ll), iii- E23 and ii-"l and adders H25 and 126 may already bepresent in the device which supplies data to the system shown in f-iG 3.This will generally be the case when the source of data is a computer ordata processing machine in such case, the pre-cxisting registers andadders in the data source may conveniently be UllllZCd.

The ertical deflection unit H LUITlpflSUS,1S shown in HG. "3,birel'ringent elements and 26 which may be crystals cut especially toallo incoming plane polarized light to pass throu h them in one path oranother as either an ordinary ray or an extraordinary ray but not bothsimultaneously. The path followed depends upon the direction in whichthe beam cnlcr ing the crystal is polarized. A beam plane polarizedperpendicular to the plane of the drawing will pass, for example,through the crystal without deflection as the ordinary ray If the lightis polarized parallel to the plane of the drawing, it will be deflectedand pass as the extraordinary ray over a different path. The spacingbetween the points at Wi'llCh the ordinary and extraordinary rays leavethe crystal is directly proportional to the thickness of the crystal Atthe input SldCS of the birefringent elements 24, 25 and 26 areclectro-optic devices 27, Bil and 29. Each of these devices is made upof an clcclro-optic crystal 30 between a pair of transparent electrodes32. When a potential of sufficient magnitude is applied across any oneof the electro-optic devices, a rotatlon of the planc of polarization ofthe light by 90" takes place For applying such a potential selectivelyacross these devices, one electrode of each device is connected toground at points 33. 34 and 35, while the other electrodes are connectetl through switches 36, 37 and 38 to one side of u potenllal source39 which is connected at its other side to ground Mechanical switchesare shown herein only to proud: an undcrstanding 0f the invention inactual practice, electronic switching means responsive to coded electricpulses would be used. The coded electric pulses would be generated bythe vertical driver B21 in response to data contained in the verticalcharacter selection register 3 E9. The potential at source 39 is ofsufficient magnitude to effect a rotation of the plane of polarizationof the light beam by as it passes through one of the clcctro-opticdevices having a potential applied across it by the closing of one oftheswitches.

The light beam i7. is supplied from a suitable source 40 through a lens41 which causes it to be collimatcd. The collimated light then passesthrough a polarizing means 42 which effects a linear polarization ofthebeam in a plane perpendicular to the plane of the drawing. A portion ofthe monochromatic, coliirnated and linearly polarized beam is passedthrough a small opening in a plate 44 to the electro'optic device 27. ifall of the switches 35, 3'7 and 38 were open, the light beam would passthrough each of the birefringent elements 2.4, 25 and 21": withoutdeflection as the ordinary ray 240, 250. and 260. Maximum deflection isobtained when the switch 3a is closed to apply a potential across theelectro-optic device 27 and the other switches are left open as shown inHQ. 4. The light beam has its plane of polarization rotated 90 by thedevice 27 and passes through the elements 24, 25 and 26 as theextraordinary ray along the paths 24m, 2500 and 26m. if the switch 3'7had also been closed, the plane of polarization would have been rotatedagain 90 by the electrooptic device 23 to pass the ordinary ray throughthe elements 25 and 26 without deflection. The total displacement wouldthen have been only that which took place in element 24, By closing theswitches either singly or in combination it is possible to obtaindeflections proportional to the thickness of any element or combinationof elements. As shown in H0. 4, the thickness of the elements 24, 25 and26 increases by a factor of two. With this arrangement, the number oflevels at which an output of light may be obtained is equal to tworaised to a power equal to the number of elements. Since three elementshave been shown, an output could be obtained at any one of eight levels.

The horizontal deflection unit H4 of the first deflector is shown inplan view FIG. 5 so the different paths that the light may followthrough this unit can be indicated. This unit includcs birefringentelements 46, 47 and 43 like those in the vertical deflection unit butrotated 90 so the extraordinary rays are deflected inwardly as viewed inFIG. 3, while the ordinary rays continue to move in planes parallel tothe plane of the drawing. At the input sides of the elements 46, 47 and48 are clectro-optic devices 49, 50 and 51 like the devices 27, 28 and29 and adapted to have potentials applied across them by the closing ofswitches 52, 53 and 54. Again, it is to be noted that the mechanicalswitches shown herein would, in actual practice, be replaced byelectronic switching means responsive, in any ol'a number of knownmanners, to electric pulses gcncrutcd by the horizontal driver 12?. inresponse to data contained in the horizontal character selectionregister 12!). Since the birefringent elements 46, 37 and 43 are turned90 relative to the elements 2d, 15 and 26, light polarized in a plane topass through the latter elements as an ordinary ray will pass throughthe elements 46, 47 and-48 as an extraordinary ray. Also light passingthrough the elements 24, 235 and 26 as the extraordinary ray will passthrough the elements 36, $7 and 42 as the ordinary ray. Light deflectedto its maximum vertical position in FIG. 4 by passing it through each ofthe elements as the extraordinary ray will pass through the elements 47and -38 without deflection if all of the switches 52, 53 and 5-3 areopen. To obtain maximum horizontal deflection of this light in H6 5,switch 52 must be closed while switches 53 and 54 are left open. Withthe deflection I units fl!) and H4 of FIG. 3 constructed as shown inNUS. 4 and 5, an output of light could be obtained from the unit H4 inany one of eight equally spaced vertical planes and at any one of eightpoints spaced vertically equal distances in each planev There are,therefore, 64 different points through which light may be directed tothe character mask 13. This number could be increased, it desired, bysimply adding another irclringent element and electro-optic device toeither one or both of Size units 110 and114.

After the light beam leaves the deflection unit 48, it passes throughthe vertical deflection unit 117 and the horizontal deflection unit 1111to the display or light sensitive medium 14 shown in FlG. 3. As is shownin more detail in FIGS. 6 and 7, the units 117 and 118 are like theunits 110 and 114, respectivcly, except that each has more than thethree birefringent elements and electro-optic devices shown for theunits 110 and 114 in FIGS. 4 and 5. The number provided will depend uponthe number of points at which it is desired to print characters bothhorizontally and vertically. if desired, only a horizontal deflectionunit may be employed in place of the units 117 and 118 so that thecharacters will be printed on a single line. A mechanism would then beprovided for advancing the medium 14 line by line as printingprogressed.

Referring again to H6. 3, assume that the light beam 12 enters the firstdeflection unit 110 at the lower right-hand corner thereof. Afterpassing through deflection units 110 and 114, the light beam will havebeen deflected upwards v increments and will have been deflectedhorizontally into the plane of the paper It increments. The quantity1'15 contained in register 119 and the quantity h is contained inregister 120. Also assume that it is desired that the beam of lightwhich comes front deflection unit 118 should impinge upon the medium 14at a location V increments from the bottom of medium 14, and Hincrements from the right-hand side of medium 14. Since the light beamwhich enters deflection unit 117 will have already been deflected vincrements in the vertical direction, deflection unit 117 must be causedto introduce an additional vertical deflection of V-V) increments inorder that the total vertical deflection of V increments may beachieved. Similarly, the horizontal deflection unit 118 must deflect abeam of light which enters it by an amount of equal to (H-h) incrementsin order that the total horizontal deflection of the light beam whichimpinges upon medium 14 will be the desired H increments. Thus, it willbe seen that, in order to furnish proper data to vertical driver 127,the adder 125 must subtract the contents of register 119 from thecontents of register 123 in order to produce the proper amount ofadditional deflection required by deflection unit 117. For the samereason, adder 126 must subtract the contents of register 120 from thecoittcnts of 124 in order to generate the proper amount ot additionaldeflection required of deflection unit 118. In theory, the numberoflocations on medium 14 upon which a beam of light may be directed isequal to the product of the beam levels produced by unit 117 and thehorizontal deflections produced by unit 118. However, it would generallynot be practical to attempt to utilize the full theoretical capability.Once the beam of light has been deflected upward by deflection unit 110,the system shown in H0. 3 is incapable of returning it to a lowerposition. Similarly, if the beam has been deflected horizontally intothe plane of the paper by deflection unit 114, it cannot subsequently bedeflected back out of the plane of the paper. Thus, the total number ofvertical locations of medium 14 that would generally be used in apractical system is less than the theoretical maximum by an amount equalto the vertical deflection which deflection unit 110 is capable ofproducing. Also. the number of horizontal locations of medium 14 whichwould generally be utilized in a practical system is less than thetheoretical maximum by the total horizontal deflection which deflectionunit 114 can introduce. 1n the ex cmplary embodiment described herein,it has been assumed that deflection units 110 and 114 are each capableof iiitroducing a maximum deflection of seven incremcnts. '1'hisrequires that a correction constant of l l l (the binary representationof the decimal digit 7) be added to adders 125 and 126. This may beaccomplished in any 01 a variety of known manners.

1n the above discussion, it was assumed that the light beam 12 entersdeflection unit 110 at the lower righthand corner thereof. However, thesystem could just as easily have been implemented in such a manner thatthe light beam 12 enters the deflection unit at the upper left-handcorner thereof. In such a case, vertical deflection unit 110 would beused to deflect the light beam in ii downward direction and horizontaldeflection unit 114 would be used to deflect the light beam in ahorizontal direction out of theplane of the drawing in F10. 3. Assumingthat deflection unit 117 is capable only of upward deflection of thelight beam, and that horizontal deflection unit 118 is capable ofdeflecting the beam only into the plane of the drawing, then it would benecessary for adder 125 to add the contents of registers 119 and 123,and it would be necessary for adder 126 to add the contents of registers120 and 124 in order to furnish proper signals to the drivers 127 and128 respectively. in this case, the sum produced in each of the adders125 and 126 would correctly indicate the additional amount of deflectionrequired of deflection units 117 and 118, respectively, and nocorrection constant will need to he added. If the light beam 12 entersdeflection unit 110 at the upper right-hand corner thereof, then adder125 would have to add the contents of registers 119 and 123, and adder126 would have to subtract the contents of register 120 from rcgister124; if the beam 12 entered deflection unit 110 from the lower left-handcorner thereof, then adder 125 would have to subtract the contents ofregister 119 from the contents of register 123, and adder 126 would haveto add the contents of register 120 to the contents of register 124. 1fan adder is required to perform a subtraction operation, a correctionconstant as defined above must also be added. 11' an addition operationis performed, no correction constant is necessary.

An example of the operation of this invention will now be given. In thisexample, it will beassumed that deflection units 110 and 114 of P16. 3are each capable of producing a maximum deflection of seven increments.Deflection unit 110 can deflect the light beam vertically upward, anddeflection unit 114 can deflect the light beam horizontally into theplane of the drawing. 1t is further assumed that deflection units 117and 118 are each capable of producing a maximum deflection of 127increments. Deflection unit 117 can deflect a light beam verticallyupwards, and deflection unit 118 can deflect a light beam horizontallyinto the plane of the drawing. Thus, for reasons described above, acharacter-shaped beam oflight can be made to impinge upon the medium 14at any location on a grid that is 121 units wide and 121 units high.Deflection units 110, 114. 117 and 118 implemented in accordance withthe above parameters are shown in more detail in FIGS. 4, S, 6 and 7,respectively. For example, assume that the character to be selected islocated at a position on the character mask 13 such that set enincrements ol'vcrtical deflection and seven increments of horizontaldeflection are required in order that a beam of light pass through theselected character. Assume further that the selected character is to beprojected upon a location on the medium 14 that is displaced from thelower right-hand portion thereof 103 vertical increments and 40horizontal increments.

In order to set the controls of the system to cause the incoming lightbeam 12 to be deflected through the selected character on the mask 13,the binary number 111 (equivalent to the decimal number 7) will be setinto each of the character selection registers 119 and 120. The binarynumber 1100111 (equal to the decimal number 103) will be set into thevertical image deflection register 123, and the binary number 0101000(equal to the decimal number 40') will be setinto the horizontal imagedeflection register 124. As shown in FIG. 4, the contents of register11) will be fed to vertical driver 121 to control the setting ofswitches 36, 37 and 38 to produce seven increments of verticaldeflection in the first vertical deflection unit 110. As shown in F10.5, the contents of register 120 will be utilized by horizontal driver122 to control the setting of switches 52, 53 and 54 to produce sevenincrcmcnts of horizontal deflection of the light beam 12 by horizontaldeflection unit 114. The light beam 12 will then pass through theselected character on the mask 13 (HG. 3).

emerging therefrom as a character-shaped beam. The beam 12, which nowcarries the shape of the selected character, will then enter thevertical deflection unit 117 shown in FIG. 5. 'v'crtical deflection unitH7 comprises seven birefringent deflection elements 139 through 135. Thefirst deflection element 130 is of such thickness as to deflect anextraordinary ray by an amount equal to one increment of deflection.Each successive deflection element 131i, 132, 133, 134, US, 136 is twicethe thickness of the preceding deflection clement. Thus, the deflectionunit 117 is capable of introducing any amount of deflection from -127deflection increments. in front of each deflection element is anelectro-optic device 137 through 143 across each of which an electricpotential may be applied by closing an associated switch T44 through339.

in order to generate the amount of beam deflection that must be added bydeflection unit 117, the contents of vertical character selectionregister its is subtracted from the contents of vertical imagedeflection register E23 by adder 125. The medium 14 (FIG. 3) is alignedwith respect to vertical deflection unit 117 in such a manner that thecharactershaped beam of light 12 must be deflected vertically upwardseven increments (and horizontally into the plane of the drawing sevenincrements) in order for the beam to be projected upon the lowerright-hand corner of the grid. The binary number lli, contained in aregister is therefore also added by adder US to produce the result whichis stored in an adder output register 152. Register 152 then furnishes aproper input to vertical driver 127 which will control the setting ofswitches 144 through 150 so that deflection unit 117 will produce thedesired additional vertical deflection of the character-shaped beam i2.After the character-shaped beam leaves deflection element 136, it willenter the horizontal deflection unit H8 shown in FIG. 7. Deflection unitUS also contains seven birefringent deflection elements 153 through I59,seven clectro-optic devices 160 through 166, and seven switches 167through 373. Adder no will subtract the contents of horizontal characterselection register Hi) from the contents of the horizontal imagedeflection register T24, and will add the correction factor contained inregister i7 3 to produce an output which indicates the total amount ofdeflection which must be added to the character-shaped light beam l2 bydeflection unit H3. This result will be stored in the adder outputregister T75, the output of which is fed to horizontal driver 123 whichcontrols the setting of switches 167 through 173 so that the horizontaldeflection unit H8 will add the proper number of deflection incrementsto the character-shaped beam l2. After the beam 12 leaves deflectionelement 159, it will impinge upon the display or light sensitive medium14 (FIG. 3) at the desired location.

As was mentioned above, various elements shown in these drawings couldbe contained in a device (such as a computer) which controls the opticalsystem. in addition to the elements previously mentioned. it will beclear to those skilled in the art that the correction registers 15!(FIG. 6) and 174 (H0. 7) could also be included in a controlling device.Also, the adders I25 and E26 could be designed in such a manner thatthey automatically add any necessary correction constant. in such acase, registers l5! and 374 would not be needed. Of course the adderoutput registers 152 and 275 could also be coritained in the controllingdevice. Additionally, various implementations of the drivers ill], I22,127 and H28 could be used Each of the drivers could contain decodingmeans which would convert an input representative of the number ofdeflection increments needed to an output which is directly indicativcof which switches must be closed in order to accom plish the desireddeflection. If the optical unit is controlled by a computer or dataprocessing machine, then the capabilites of the controlling device couldbe utilized to convert deflection information into switch-settinginformation. For example, such a controlling device could convert thedeflection infor mation into a pattern of binary ones and zeros whichare directly indicative of the switch settings required for the desireddeflection. ln such a case, the drivers could be relatively simpleelectronic devices which control the various switches.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

I claim:

1. An electro-optic printer comprising, in combination:

means for providing a beam of collimated, plane polarized light;

means for forming said beam, at a selected point, into acharacter-shaped beam having the shape of any desired character;

first position indicating means for indicating the point at V which saidselected character has been formed;

a sheet oflight sensitive material;

second position indicating means for indicating a selected position onthe surface ofsaid light sensitive material; and

directing means responsive jointly to said first position indicatingmeans and said second position indicating means for directing saidcharacter-shaped light beam to said selected position on the surface ofsaid light sensitive material.

2. The apparatus ofclaim 1 wherein:

said first position indicating means comprises means for manifesting adigital signal representative of the displacement of saidcharacter-shaped beam from a predetermined zero position; and

said second position indicating means comprises means for manifesting adigital signal representative of the displacement of said selectedposition on the surface of said light sensitive material from apredetermined zero position.

3. The apparatus ofclaim 7. wherein:

said directing means includes adding means for adding the digital signalcontained in said first position indicating means to the digital signalcontained in said second position indicating means.

4. The apparatus ofclaim 2 wherein:

said directing means includes substracting means for subtracting thenumerical quantity represented by the digital signal in said firstposition indicating means from the numerical quantity represented by thedigital signal contained in said second position indicating means toobtain a digital signal representing a resultant quantity.

5. The apparatus of claim 4 wherein:

said directing means also contains means for adding a predeterminedconstant to said resultant quantity.

6. An elcctro-optic printercornprising, in combination:

a mask having transparent portions in the form of characters to beprinted;

means for producing a beam of linearly polarized light;

first position indicating means for manifesting a digital signalrepresentative of the position on said mask of a selected character;

first deflecting means responsive to said first position indicatingmeans for deflecting said beam of light to said location of saidselected character, whereby a character shaped beam of iight is passedthrough said mask in the shape of wit! selected character;

a sheet of light sensitive material;

second position indicating means for manifesting a digital signalrepresentative of the position of a selected location on said lightsensitive material;

deflection control means responsive jointly to the digital signalscontained in said first position indicating means and said secondposition indicating means to produce a resultant deflection signal; and

second deflecting means responsive to said deflection control means fordeflecting said character-shaped beam to said selected location on saidlight sensitive material.

7. The apparatus ofclaim 6 wherein:

said deflection control means comprises a digital adder 8. The apparatusofclaim 7 wherein:

said deflection control means l'urther comprises means for adding apredetermined correction constant to said resultant deflection signal.

9. An electro-optic printer comprising, in combination:

a mask having portions in the form of characters to be printed;

means for producing a beam of linearly polarized light;

first horizontal position indicating means for manifesting a firstdigital signal representative of the horizontal displacement of aselected character on said mask from a predetermined zero position onsaid mask;

first vertical position indicating means for manifesting a seconddigital signal representative of the vertical displacement of saidselected character from said zero position on said mask.

first horizontal deflecting means responsive to said first digitalsignal to horizontally deflect said beam of light by an amount equal tosaid horizontal displacement,

first vertical deflecting means responsive to said second digital signalto vertically deflect said beam of light by an amount equal to saidvertical displacement;

said beam of light, after deflection by said first horizontal andvertical deflecting means, being formed by said mask into acharacter-shaped beam carrying the shape of said selected character;

a light sensitive medium having on its surface a selected location uponwhich it is desired that said character-shaped beam shall impinge;

second horizontal position indicating means for manifesting a thirddigital signal representative of the horizontal dis placement of saidselected location from a predetermined lil zero location on said medium;

first adding means for combining said first and third digital signals toproduce a resultant horizontal deflection signal; and

second horizontal deflecting means responsive to said resultanthorizontal deflection signal to horizontally deflect saidcharacter-shaped beam to a location that is horizontally displaced fromsaid zero location on said medium by an amount equal to said horizontaldisplacement of said selected location on said medium;

whereby said character-shaped beam will be directed to a selectedhorizontal location on said medium.

10. The apparatus ofclaim 9. further including:

second vertical position indicating means for manifesting a fourthdigital signal representative of the vertical displacement of saidselected location from said zero location on said medium;

second adding means for combining said second and fourth digital signalsto produce a resultant vertical deflection signal; and

second vertical deflecting means responsive to said resultant verticaldeflection signal to vertically deflect said character-shaped beam to alocation that is vertically displaced from said zero location on saidmedium by an amount equal to said vertical displacement of said selectedlocation on said medium;

said character-shaped beam, after deflection by said second horizontaland vertical deflecting means, being directed to said selected locationon said medium.

